1. Talk with your advisor and/or the faculty member who will serve as your dissertation committee chair. She or he will have a good idea of your capabilities and of the kind of topic that will be received favorably by your university.
2. Read, read, read. Look at the most recent issues of the scholarly journals in your field as well as any recent books in the field. Pay particular attention to the "discussion" and "conclusion" sections of journal articles, as these often include the author's assessment of the need for future research. Often, scholarly authors will specifically say that a particular topic needs to be researched or that a particular study needs to be replicated or done in a different way. Also look for recent review articles that summarize recent research in your field, again looking for hints as to what still remains to be learned.
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